The History of Rome (1.17.6-1.17.10)

Ten therefore were in office, but only one at a time had the insignia of authority and the lictors. Their individual authority was restricted to five days, and they exercised it in rotation. This break in the monarchy lasted for a year, and it was called by the name it still bears —that of “interregnum.”

After a time the plebs began to murmur that their bondage was multiplied, for they had a hundred masters instead of one. It was evident that they would insist upon a king being elected, and elected by them.

When the senators became aware of this growing determination, they thought it better to offer spontaneously what they were bound to part with, so, as an act of grace, they committed the supreme power into the hands of the people, but in such a way that they did not give away more privilege than they retained.

For they passed a decree that when the people had chosen a king, his election would only be valid after the senate had ratified it by their authority. The same procedure exists to-day in the passing of laws and the election of magistrates, but the power of rejection has been withdrawn; the senate give their ratification before the people proceed to vote, whilst the result of the election is still uncertain.

At that time the “interrex” convened the assembly and addressed it as follows: “Quirites! elect your king, and may heaven's blessing rest on your labours! If you elect one who shall be counted worthy to follow Romulus, the senate will ratify your choice.”